Zirconium oxide and method of making same



July 2, 1940 c. J. KlNzlE Er Al. *y 2,206,287

ZIRCONIUM OXIDE AND METHOD OF'MAKING SAME Filed Feb. 2. 1937 2 Sheets-Sheet 1 PETROLEUM :j amr/12025 HEHRTH CHBLE ENOVABLE 5f6770/V WATER EEMOVABLE 5Ec/0/v- WATER BY PUNHLP /(E ATTORNEY.

i* tured `zirconium oxides.

Patented July z, 1940 PATENT `OFFICE zmcoNlUM oXIDE AND METHOD or MAKING sinus Charles J. Kinzie and Donald S. Hake, Niagara` Falls, N. Y., assignors to The Titanium Alloy Manufacturing Comp i corporation of.Maine any, New York, .N. Y a

Application `February ys, 1937, serial No. l123,588 1e claims i (cies- 2n f "Our invention relates moreparticularly to the 3 production of synthetic baddeleyite `of a particle `sizerange and degree of purity heretofore nonl i existent either in nature or in various manufac- We accomplished this improved result in the electric resistance furnace Withthe incidental productionot silicon carbide as a oy-product.

`Our invention consists primarily in `the discoveiy that `from zircon (ZrSiOi), .an` essentially silicon-free, crystalline vzirconiuni oxide in the i forin `of a substantially chemically pure synthetic `baddeleyitemay be made, `While at thesame time volatilizing essentially alltl'xe iron contained in i the zircon.` While accomplishing 'this result,

there isalso formed in the same furnace a sub- -starltial yield of` silicon carb-ide, .a` portion of "which may be the productof the silicon volatilizedfrom the zircon, While the remaining'portion` Dief such silicon carbide is produced in the in sulatingfmix consisting preferablyof petroleum Qokasiiica sand and sawdust the absorption of waste heat from the `zirconium reaction zone or innerzone of the furnace.

` `I-Ieretofore in the' `production of zirconium oxide, soiencewhas had to `depend upon various relatively complicated chemical separations involving preliminary fusions of zirconwith alkali andsubsequent treatments with acid andvarious otherlatersteps, such as crystallization, in order `to separate the zirconiurnoxide fronicombined and other impurities such as Vsilica which is'combinedvvith `zirconia in the zircon (ZrSiOfi).

Other 'impurities such `as iron, titanium, rare `earth compounds,retc.have also been separated fromithe zirconium-containing materials onlyby relatively `complicated procedures. i

Accordingto our improved methods the zirconium-containing material is at no stage .40 brought into solution, nor isfthe raw zirconium material decomposedor altered bythe aid of fusion or-other decomposing agents. As a` result `of our discoveries upon which claims for ournew and improvedproduct are i -45 based,` We obtain 4a zirconium oxide in form of crystals and crystal aggregates of particle size heretofore unknown either in nature or in `any of `the `manufactured zirconia products.

Thel optical constants, crystal structure `and 50` X-ray` diraction patterns are those of Z102 baddeleyita but differ from known products in particle size as well as in purity.

Natural baddeleyite cannot be used for reiracn Vtories for temperatures above 1800 to 2000 C.

due to the facty that the impurities therein re- "51 sult in deterioration `under heat, While manufaci tured zirconium oxides `are unsuited for a variety of reasons; Vinsome the particle size is such as to result in excessive shrinking upon heating, i, While in otherstraces of carbides `result in ex-v 10 pansion. i

` Our new 'and improved zirconium oxide, in form of the novel particle size range, fabricates directly into very dense refractory shapes havingupon heating to very hightemperatures practicallyno shrinkage, and having also a very high i meltingpoint by virtue of its `freedom from impurities; and being free of carbides 'it does not tendto Yexpand and vdisruptupon heating.

'This result isobtained by heating practically 20 pure 'Zircon (ZrSiO4) in form of grains ranging in 'size from Vabout 30 mesh to 200 mesh in ian electric'resistance furnace, but 'out of direct contact with carbon. The Zircon is decomposed, the silica is volatilized and `completely lexpelled along 25 with traces of iron and some other impurities in-` cluding P205, from the residue of zirconia which remains as a slightly sintered aggregate of zirn conia crystals, and lcontains 'a small amount of 4zirconium carboxide due to contact of the Zircon 30 chargewith adjacent carbon and possibly, also, to a slight eect of carbon gases.` The product Y herein claimed is then formed by calcining the` zirconia furnacedischarge vin air to oxidize the smalllamount of zirconiumcarboxide to extreme- 35 ly ne ZrOz, land then removing same from the relatively coarse `desired ZrOz byany suitable means, such as air classicatio-n, elutriation, etc., after `reducing the product tofabout mesh,`

`This new artificiallyfprepared baddeleyite (zir- 40 conium oxide) is in the form ofa dense crystalline material, and as so `produced constitutes an excellent base :for making superrefractory materi'alandarticles of zirconia.

Bysubjecting'our productzto 4finishing processes 45 `such `as describedin U. S.'Patent 1,588,476 dated l June 15, 1926,1to Kinzie, an ,excellent White opacifyingpigment for vitreous enamels, glazes and other applicationsmay 'readily be produced.

' the following -materials suitable neness without any other treatment, yis an excellent opacifier pigment that is creamcolored, but is free from the defects of zirconium oxide produced by other electro-thermal processes, such as the presence of dark-colored blemish producing particles not removed by simple oxidation.

Our invention is based, in part on the discovery that by heating zirconium silicate in the absence of carbon in an electric resistance furnace, the silicon compounds are completely Volatilized, and in addition irony compounds are also volatilized so as to leave practically only a trace 0f same in the resultant zirconium voxide product.

Starting with a relatively purer zirconium sili cate, there is left a mass consisting of practical- Upon ignition the ly pure zirconium oxide. mass does not change in .volume and-"the small amount of carbon compound presentl is eliminated so as to leave the zirconium oxide as fa cream-colored material.

Of the drawings showingfdifferent `l'iygolesl of electric furnaces and method of loading saine," Fig. l is a sectional elevation showing-Lone rrtype Fig. 2 is a section takenon the line 2-2 of Fig. 1; I

Fig. 3`is afsection taken on the ,line 3-3- of Fig. 1; l

Fig. 4 is an enlarged perspective View of the granular graphite resistor partly broken away; Fig. 5 isan enlarged fragmentaryhorizcntal sectional View of a modified form of furnace; and Fig. 6 isa detail enlarged sectional View on the. line 6 0 of Fig. 5. I

The following example will serve vto show how' our methods can be practiced to produce this novel zirconium oxide product,land will also include a description of the .characteristics and-` properties which differentiate this product from natural badd'eleyite as wellas from-prior syn-v thetic zirconium oxides. v v

Eample A.-The `following complete example will serve to show how our methods may be used to produce' our new zirconium oxide. productand.

a by-produot of silicon carbide (SiC).H The furnace as shown in the. accompanyingdrawings vwas loaded in the following-manner. .fr u

An insulating mix is rst prepared `by .mixing vPartsgby l .weight Green petroleum coke 1, 37 Silicon.sand K. Wood sawdust v8 Other forms of carbon may be used in place oi petroleum coke such as coal or calcined coal in the form of foundry coke, if desired.

This mixture is charged upon the vhearthfof the furnace to a depth of about ten inches and leveled off, and then in center overV an areaof about ifteen inches by six inches a piece of `thin tough paper was placed. i

The graphite electrodes consist preferably of round one inch by twenty-six inch long pieces, one through each end wall, the exterior ends being suitably connected to the source of'electric current, while the ends within the furnace are brought towithin thirteen and one-half inches of each other, leaving this thirteen and oneehaif inchspace for the placing ofthe granular graphe ite resistor.V At eachi'endof the roundV one inch lcon sand of the following composition.

graphite electrodes is a three inch by three inch by one inch block of graphite to confine the zones of Various materials.

rIhe insulation between the blocks of graphite was covered with a sheet of thin tough paper. On this paper was placed a one-half inch layer of granular green petroleum coke, two and one-l rvwas placed.

Outside the furnace the ends of the graphite r electrodes may be cooled by passing a current of water through them as shown in Figs. l and 2.

Then sheets of thin tough paper were arranged, 4one on each side, one-half inch away from the sheets confining the granular graphite core, and these two spaces Were 1'i1led with zir- Per cent zirconium silicate 98.50V Iron impurity (calculated as FezOs) f. .0l Titanium impurity (calculated as TiOz) .02

Balance impurities such as free SiOz, rare' earths, P205, etc 1.47v

. l 100.00 Therewas then arranged one-half inch away from the paper coniining the zircon, other sheets of paper andjin the space so formed is placed granular green petroleum coke. A one-half inch layer. of granular 'green petroleum coke `was then placed to cover theconfined charge as shown in Fig 4, and the entire remaining'space in the furnace was then filled with the mixture of coke,

sand and sawdust as used at the bottom (Figs.

1 and 3).

The graphite electrodes extend in through iurnace. wall, and are connected inside with a onehalf inch wide by three inches high by thirteen;

and one-half inch zone of granular graphite. At each sidev of this granular graphite core-is a zone of zirconsand thirteen and one-half inches long, one-half inch wide, and three inches high. kOutside the zircon and graphite resistor zones is an envelope oi petroleum coke thirteen and one-half inches long by one-half inch thick.

The granular graphite core, the zircon, andv the coke are asa whole temporarily separated from the insulating mix at the bottom, sides and top by layers of paper, and ,at Vthe ends by the contact blocks of graphite (Figs. 2 4). The charge is therefore completely lsurrounde at the bottom, sides,` top and ends with approximately twelve inch zoneof this insulatingcharge.`

amperes, which developedga temperature sufli-v ciently high to dissociate the ZrSiO4 and Volatil` ize the silicon as well as to form SiC in the acljacent zones of the furnace. The temperature' probably is between about 2200 and 2700 C., probably about 2500o C. in the core.

As the run progressed, the carbon-monoxide gasevoived `was, ignited atvariousgpqnts atthe,

` gregates of coarse crystals.` 40" This gray-colored` mass upon calcination. changed1 quickly to a` cream-colored material without increasing or `decreasinglnovticeably as regardsvolume; andwithout materially effecting 45s.! the structure i of l the constituentzirconium oxide.

sideslsendsf` and bottom` ofy thevfurnace. The ex teriorl of the; furnacel bottom' hearth,; sidef walls,; or topaoftheinsulating mixV were never much above# room@ temperature,` and: thewarmth at `51@ `these'points was mainlyI the result of the burning` ofcarbon monoxide or other `gasespurposely ignited from the` outside. so as'to converti same intoxharmlessgases;

i Afterfl/g: hours, the current was turned ofi" 10 and` `furnace `and its` charge was. allowed' toycool for about '72 hours.

The top" and side insulations were removed therebyV exposing an.` envelope or shelly of` greenishl' colored` crystals, which i upon; analysis.` pr'oved" 15` `tofA consist mainly of crystals of silicon. carbide.

(SiC-ll, a well-known` abrasive` and refractory material.

carbide occupying the zoneswhich formerlycon-v sistedfof thelay'ers of-A petroleum coke, this sili`` con carbide having been formed apparently' by the i silicon materiali as? it lwas. volatilized from the zircon; which siliconimaterial combined withl the` coke to form siliconfcarbida 2li F` {rn-luie zene eriginenylf111edwith thel` zireen sa-ridwe found aA friablegrayco1ored masscone "sisting of zirconium oxide containing a small amount' of zirconium carboxide, the total c'arb'ofn'` content of the mass being about 0.10 percent'.`

The,4 zirconium oxide-so` produced contained by analysis: i Percent Silicon (calculated as SiOz)` -v f Nilm, Titanium` (calculated asTiOz) 0.030 Iron (calculated as Fe2O3) A 0.002 zirconium oxide 99.568*` Others-'rare earths, traces A1203,` etcf. I 0.400

l Using-,the'product as herein prepared-1 and described the `following observations were` made:

J Acream-colored granular powder which con`` omsists` almost exclusively of aggregates ot crystals `showing lamellar twinning.` The` lalmellael arevery rarely more than.02` long, and` the;v bulkofthem are` .005 to .015 mm. intlength. The refractivef index, is ^y---,2.2` andv a--2l12, which` as@ are characteristic of baddeleyite.

l `A trace of other grains arepresent. These consist of crystalstoo minute to determinein a matrix that `is either glassy: or` too minutely `crys-` tallinel to resolve microscopically. The aggre-i 70; gate refractive` index is somewhat variable andre deiinitely," but" not greatly lower than fori the coarse; crystals namely, about 2.0.

TheQabove crystal size` observations werei ofi course `those of clearly individual crystal aggrew l5 gates in* the: larger `masses and-,separate crystals;

Uponlremoval of this outer` shell-` oil silicon carbide,` We found two z'onesiofir silicon of a microscopeequippediwitha' camera; A pho# tograph' was made of a micrometer representing denite dimensions and separate photographswere made of a number of mounts of our product atsame magnification `as that used in photographing, the micrometer. By using a piece of transparent Cellophanathe micrometer print lines' were lined on the Cellophane sheet over the photographs of ZrOz particles and it was possibleto; measure as well as count the particles in a eld.

This method we have used to advantage in particle size determination and ndit quite reliable.

in the smallersizef range" were l observed by' means Based onthis method the `following numerical count as representing the number of each size" particle present in this product was obtained and based on` thisl numerical count the particle size distribution in terms of percent byweight was calculated. both resultsare presented in the following:

" Mean Numerical size range size count Percent' Our new productv then `consists ofl zirconium oxide of the crystalslze` asshown by the micro-` scope and inthe state of aggregation as expressed by thelforegoing: particle size distribution,. chemical purity, etc.

X-ray' studies'` havel been madecomparing. the` ZrOz product of this case with the ZrOzvof our companion caseiiled` March l,` 1934, Serial No. 713,536, now Patent 2,110,733, and with areagent iormioi ZrOz whichy islcom'monly'usedl.

i The diffractionpattern of ZrOz of our Patent` No. 713,536, gave broad ZrOr 2,110,733, Serial lines showing presencev of ZrOe particles too small tof bei clearly seen-.with the microscope. The "dife fraction patternoffZr'Oeof this caseshowed` that the particles were" almost exclusively those of ZrOcl of suchl size as to be easily determinable' The' diffraction lines of with the microscope. the reagent ZrOaagr'eed with lines of' the ZrOz product as'our companion case, except that in` the pattern for' the reagent Z'rOz, afewiaint lines `s1f1"`ovv`ednot seenlin othersl and w re presumably due' to` impuritiesv not presentA in' the respective Z'rO`2 products of this andv our Patent 2,110,733,

Serial No: 713,536", y y

Hence by' combining theevidence of chemical analysis the microscope, and the Xray films,

we conclude and assertthat the Z102 ofrthis case consists almost wholly of crystals of'loaoldeleyite` of such sizes asto be oleterrninableY with the microscope, andthat `the ZrOz claimedin our Patent 2,110,733 `consistsmofl a mixture oi minute crystals of ZrOzV in glass. Since the analysis showsA mainly ZrO2,.then the. glass in which mi nute ZrOz crystalshave formed is aA pure ZrO2I glass or vitreousfZrOzas setforth in ourPatent 2,110,733. Byway ofi comparison theV following` chemical analysis of` what must have` been aA carefully selected specimen ofV baddeleyite the` purestiound-y infr nature in `pelololerform,` was as follows (Mele `viz: 2700-2900 C. baddeleyite, even when finely` milled, is at best lors Treatise Inorganic Chemistry, vol. VII, pages' 122,v 123, Titanium, `Zirco'nium, etc.)

Percent ZrOz 96.52 y, SiOz 0.70

A1203 0,.43 F8203 0.41 CaO 0.55' MgO 0.10 NaKO 0.42 Loss on ignition 0.39

- Mellor also states thatl the `pebbles of baddeleyite from Brazil classified and showed the analyses as follows:

Red and raler-ed Rggh Gld Vlflegus fnable and hard hard dem@ `glassy Therefore it is obvious that the processes in nature have never produced a zirconium oxide even remotely approaching our improved zirconium oxide in purity.

All natural forms of ZrOz as shown in Mellor start to melt at 2000 C., and are limited in their refractory properties due to the associated impurities, while our new pure synthetic mineral has the very high melting point of the pure oxide The purest natural form of a brown-colored material which cannot be used.

to bring about the pure white effect which our` novel synthetic ZrOz produces when embodied in enamels, glazes and general `pigmenting ap- .plications This Example A shows that by means of our new methods a pure synthetic baddeleyite (ZrOz) may be produced directly from ZrSiOr, and that the silicon evolved has been converted to the useful silicon carbide, while the heat after accomplishing its major function has been effectively used to form additional -silicon carbide fromI the inner zones of insulating mix.

We do not wish to conne our methods of charging the furnace to that specically described in foregoing ExampleA. For instance, the zircon may be placed below and above the core of granular graphite as well as at the sides.

The Zircon may also be arranged in suitable containers such as paper or cardboard cartridgesl which are placed adjacent the core and are surrounded with coke. Graphite or carbon containers may likewise be used to hold the zircon charge, and maybe simply removed and discharged after the reaction is over and the charge cooled. e

We` do not wish to coni-lne ourselves to' the use o'f granular carbon as the core material; any suitable conductor, such as graphite or carbon rods or mixture of same, may be4 used as thev resistor with satisfactory results.

In case it is desired to burn out the small amount of carbonaceous material the furnacev maybe opened while charge is still hot and the small amount of carbon compounds allowed to oxidize in air of its own heat. f

To'the best of our knowledge we have discovered and produced an improved zirconium oxide suitable as a refractory material for vhigh temperatures; alsov for use as an opacier in enamels,

etc. as well as a practical chemically pure reagent ZrOz which has been produced directly from' zircon without chemical or fusion treatments.

We have thereby not only effected a marked advance in the zirconium art byway of producing a novel pure zirconium oxide at a cost much' lower than for all other zirconium oxide processes, but also have additionally produced silicon carbide in the same furnace which additionally reduces the cost, since this SiC is also a useful" product.

In addition to being suitable as a high temperature refractory an opacier and as a pure zirconium constituent for glass and enamel compounding, our new synthetic zirconium oxide product is a useful material in the production of pure zirconium compounds, sulphates, uorides, etc., since unlike the zircon (ZrSiOr) from which itwas made, our new and improved zirconium oxide is soluble in concentrated sulphuric and hydrofluoric acids.`

Related subject matter is disclosed and claimed in our Patent 2,072,889, issued March 9,v 1937.

We claim as our invention: I

1. A. calcinedessentially silicon-free crystalline zirconium oxide in the form of synthetic baddeleyite obtained by the electrothermic decomposition of zirconiumsilicate without being in intimate contact with carbon with substantially complete expulsion of silicon compounds and consisting of a granularproduct composed.`

ofmore than 99.50% ZrOz and traces of iron and titanium, the crystal particles and aggregates thereof being microscopically determinable and having a particle' size range from 5 to 80 microns with a melting vpoint between 2700 to 2900 C.

2. A calcined essentially silicon-free crystalline zirconium oxide in the form of synthetic baddeleyite'obtained bythe electrothermic decomposition of zirconium silicate without being in intimate contact with carbon with substantially 'complete expulsion of silicon compoundsl and Vconsistingv of more than 99.50% ZrOz and traces of iron and titanium, and characterized Vand consisting of a granular product composed of more than 99.50% Zr02 and traces of ironr and 'titanium and showing lamellar twinning ranging from 0.005 to 0.02 mm. in length, thecrystal particles and aggregates thereof being microscopically.determinable and having a particle' size range from 5 to 80 microns with a.

melting point between 2700" and 2900 C.

4. A calcined essentially' silicon-free crystalline zirconium oxide in the form of synthetic baddeleyite obtained bythe electrothermic `decomposition of zirconium silicate without being?.

in intimate contact with carbon with substantially `complete. expulsion of silicon compoundsf and consisting of more than 99.50% ZrOz'and traces of iron and titanium, and characterized asr being a granular cream-colored powder, and showing lamellar twinning ranging from 0.005 to 0.02 mm. in length, the crystal particles and c y 2,206,287 aggregates thereorfbeiag microscopicany 'determinable and having a particlesize range from` tojS'O microns with `annelting point between i 5. A calcined essentially silicon-free crystalline zirconium oxide in the `form of `synthetic baddeleyite obtained `by theelectrothcrmic de- .i composition of ``zfirc`clniium silicate without being in intimate contact with carbon with substan- `tially complete expulsion of silicon compounds andj consisting of a granular productcomposed 270m and 2900 c.

of more than 99.50% ZrOz, the crystal particles and aggregates thereof being microscopicallyl determinable and having a particle size range from 5 to 80 microns with traces ofiron and `not over i melting point between `ofmore than 99.50% ZrOz and showing lamellar twinning rangingfrom 0.005 `to, 0.02 mm. 'in

`length, the crystal particles vand aggregates p `between 2700 to 2900 thereof being microscopically determinable and having a particle size range from 5to 80 microns with traces of iron andnotover 0.10% of titanium with a melting point` between 2700i and `'7. A calcined substantially chemically pure synthetic baddeleyite obtained by the` electrothermic decomposition of zirconium silicate without being in intimatecontact with carbon with `substantially complete expulsion ofsilicon com-h pounds and consisting of crystals and aggregates thereof being microscopically determinable and having a particle size range from 5 to 80 microns thereof being microscopically determinable and.

having a particle size range` from 5 to 80 microns `with traces of iron and not over 0.10% of titanium with a melting point between 2700 and 2900 C.

9. A calcined substantially chemically pure synthetic baddeleyite obtained by the electro-1 i thermic decomposition of zirconium silicate without being in intimatecontact with carbon with substantially complete expulsion ofsilicon compounds and consisting of crystals and aggregates thereof being microscopically determinable and showing lamellar twinning rangingfrom 0.005`

to` 0.02 mm. in length `andhaving a particle size range from 5 to 80 microns with a melting point 10. A` calcined essentially silicon-free crystalline zirconium oxide. in the formof synthetic baddeleyite obtainedfby the electrothermicde-` composition of l zirconium silicate without being in intimate contact withcarbon with substantially complete expulsion of silicon compounds and with a melting point above 2700` C. and characterized as being a granular cream-colored powder, the crystal particles `and aggregates thereof being microscopically determinable and having a particle size range from 5 to 80 microns.

131. A` calcined essentially silicon-free crystaljecting said zirconium line zirconium oxide" in the form of f, synthetic baddeleyite obtained by the electrothermic dein intimate contactwith carbon with substantially complete expulsion of silicon compounds i `composition of zirconium silicate without being.,

and with a melting-point above 2700" C. and

characterized as being a granular cream-colored powder, the crystal particles `and aggregates thereof being havinga particle size range from 5 to 80 microns with a titanium content not over 0.10% and traces of iron compounds as an impurity therein.

12. The method of making a crystalline synthetic baddeleyite consisting of more than 99.50% Zr02` the crystal particles and aggregates thereof having a particle size range from 5 to 80 microns from zirconium` silicate, which comprises subsilicate to electrothermic decomposition without being in intimate contact with carbon with substantially complete expulsion of silicon compounds, crushing the zirconium oxide residue to about `40 mesh and calcining same to convert the small amount of zirconiumcarbon compounds therein to ultra-microscopic zirconium oxide grains, and then separating said grains from the relatively coarse crystalline synthetic baddeleyite of said specified particle size.

13.` The method of making a crystalline synthetic baddeleyite consisting of more than 99.50%

` Zr02 the crystal particles and aggregates thereof having a particle size range from 5 to 80 microns from zirconium silicate, which comprises subjecting said zirconium silicate to electrothermic decomposition Without being in intimate contact with carbon with substantially complete expuloxide residue to about 40 mesh and calcining same under oxidizing `conditions-to convert the small .amount of zirconium-carbon compounds `therein to ultra-microscopic zirconium oxide grains, and then separating said grains from the relatively coarse crystalline synthetic baddeleyite cf said specied particle size. y

14. The method of `making a crystalline zirconium oxide from zirconium silicate which comi. prises heating said silicate enveloped in an insulating mix in an electric resistance furnace with substantially complete expulsion of silicon compounds, crushing the resulting mass toabout 40 mesh, and calcining the massso as to produce a granular product composed of microscopically determinable crystals` consisting of said zirconium oxide more than 99.50% c `synthetic,baddeleyite with traces of titanium and iron therein consisting of ZrOz in the form of microscopically determinable crystal particles and aggregates having a particle size range of from 5 to 80 microns.

15. The method of making a crystalline zirconium oxidefrom zirconium silicate which comprises heating said silicate without being in intimate contact with' carbon and enveloped in an insulating mix in an electric with substantially complete expulsion of silicon compounds,` crushing the resulting mass to about 40 mesh, and calcining the mass so as to produce a` granular product composed of microscopically determinable crystals consisting of said zirconium oxide more than 99.50% ZrOz in the form of synthetic baddeleyite kwith traces of titaniumand iron therein consisting of microscopically determinable crystal particles andaggregateshaving'a particle size range of from 5 to 80 microns.

16. `The method of 'making a crystalline zirconium oxide compound from crude Zircon which microscopically determinable and i resistance furnace sion of silicon compounds, crushing the zirconium i Y ance furnace with substantially complete expul- :sion of silicon and iron compounds, then removing the silicon carbide formed, crushing the resulting massto about 40 mesh, andcalcning the resulting material-under oxidizing conditions to convert the'bulk thereof into a crystalline Zirconium oxidel compound in' the form of synthetic baddeleyite substantially free from silicon `and having a titaniumV content not over 1% consisting of microscopically determinable crystal particles and aggregates having a particle sizey range .of from 5to 80 microns. y l

` CHARLES yJ. KINZIE.

DONALD s. HAKE. 

